1. Field of the Inventions
The present inventions relate to steering methods and steering systems for boats.
2. Description of the Related Art
Boats with a marine propulsion unit such as outboard motors and stern drives (hereinafter simply referred to as “outboard motor”) mounted to the stern have a steering device with which the outboard motor is pivoted to the left and right of the hull for steering control.
An electric steering apparatus using an electric motor as a steering device for an outboard motor is disclosed in Japanese Patent Document JP-B-2739208. In this electric steering system, the external forces imparted to the outboard motor are not applied to the steering wheel during boat operator's steering operation. Thus, the boat operator is not provided with a steering feeling in response to such external forces, i.e., a heavy or light feel of the steering wheel depending on steering speed or steering angles, or a steering feeling caused by the external force such as wind or waves. With this lack of feeling of the steering system during steering, the boat operator is less able to detect and react quickly to such external forces. As such, it is more difficult for the operator to compensate for the effects of these forces on the movement of the boat.
Japanese Patent Document JP-B-2959044 discloses a steering method in which a reaction torque is applied to the steering wheel in response to a steering angle allowing for external forces caused by the rotation of a propeller of the boat (known as the “paddle-rudder effect” or the “gyro effect”). In this steering method, the reaction torque to be applied is not optimum to the attitude and speed of the boat or the behavior of the boat related to a yaw rate and lateral acceleration, making it difficult for the boat operator to realize the operating conditions and respond appropriately and promptly to the behavior of the boat as influenced by the external forces.
A steering apparatus for an automobile is disclosed in Japanese Patent Document JP-A-Hei 10-226346. This steering apparatus also includes a reaction force motor. This system calculates a reaction torque to be applied to the steering wheel based on detected vehicle speed, yaw rate and the like, and causes the reaction motor to apply a reaction force.
Since boats are designed to float on water and to apply thrust to the hull via the water in which they float, the behavior of such boats are unlike that of automobiles and thus are unique. Therefore, it is impossible to apply the steering device disclosed in Japanese Patent Document JP-A-Hei 10-226346 directly to the boats to implement the application of reaction torque.